Lubricant compositions for motor vehicle transmissions

ABSTRACT

The disclosure relates to a lubricant composition including: (a) an organomolybdenum compound, (b) one or more anti-wear and extreme pressure additives chosen from thia(di)azoles, (c) one or more phosphorus-containing or phosphor-sulfur-containing anti-wear and extreme pressure additives chosen from phosphites, phosphates, phosphonates, thiophosphates or thiophosphites, the lubricant composition having a weight content of molybdenum between 90 and 350 ppm. This is used for lubrication of gear boxes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International Application No. PCT/IB2011/052801, filed on Jun. 24, 2011, which claims priority to French Patent Application Serial No. 1055108, filed on Jun. 25, 2010, both of which are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to lubricant compositions, in particular for automobile transmissions, particularly lubricant compositions for manual gear boxes.

TECHNOLOGICAL BACKGROUND

Transmission components of automobile vehicles operate under a high load and at high speeds. Oils for these transmissions should therefore be particularly performing in protecting the parts against wear and fatigue, and notably protect gear teeth against the flaking phenomenon. Flaking occurs after a long ageing time, preceding visible deteriorations. The mechanisms are not well known, but the phenomenon starts by initiation of cracks at a certain depth under the surface, these cracks propagate and when normal cracks are generated at the surface, flakes are suddenly detached.

The prevention of this phenomenon requires a reduction in the contact stresses by means of a suitable geometry of the parts, and by reduction of friction, while avoiding adhesion. The lubricant is involved in this prevention process, mainly by the physic-chemical reactivity of its additives. Generally sulfur, phosphorous, phosphor-sulfur or borate anti-wear and extreme pressure additives are added in order to provide the transmission oils with properties which are protective against flaking. The other additives present in the lubricant may also have a positive or negative impact on the propagation of cracks inside the parts and therefore on the flaking phenomenon.

In manual gear boxes, the presence of synchronizers induces additional stresses. Actually, these components include a cone and ring device between which frictions have to be specifically controlled: the friction should be sufficient for synchronization of the gears, but the cone and the ring must have then have the possibility of disengaging, because otherwise blocking of the synchronizer takes place. Moreover, if the friction level is not adapted to the geometry of the parts, wear occurs on the cone-ring assembly.

The friction level may be adjusted by adding friction modifiers in these oils for gear boxes. Thus, in oils for manual gear boxes, anti-wear, extreme pressure additives and friction modifiers may co-exist, all having an action at the surface of the parts and potentially an effect on both the friction level and the flaking phenomenon. The oil formulation for a manual gear box having both high protection against flaking, avoiding wear and blocking of the synchronizers and allowing easy changing of gears, is based on a selection and specific dosage of the friction modifiers, of the anti-wear and extreme pressure additives.

It is known how to formulate lubricant compositions comprising organic molybdenum friction modifier compounds with organic phosphorus and/or organic sulfur and/or organic phosphor-sulfur anti-wear and extreme pressure compounds, in particular in order to improve the anti-wear properties of these oils. U.S. Pat. No. 6,806,241 discloses a lubricant composition comprising a molybdenum complex prepared by the reaction of 1 mole of a fat which may be a glyceride or a fatty acid, of 1 to 2.5 moles of diethanolamine, and of a molybdenum source in a sufficient amount in order to obtain a complex containing from 0.1 to 12% by weight of molybdenum based on the weight of the complex, a thiadiazole compound and optionally a phosphorodithioate. No specific example is given of a composition comprising both molybdenum, at a mass content comprised between 90 and 350 ppm, sulfur and phosphorus.

EP Application 0874040 discloses lubricants for internal combustion engines comprising a molybdenum complex prepared by the reaction of 1 mole of fat which may be a glyceride or a fatty acid, of 1 to 2.5 moles of diethanolamine, and of a molybdenum source in a sufficient amount in order to obtain a complex containing from 0.1 to 12% by weight of molybdenum based on the weight of the complex, and of an organic sulfur compound selected from dimercaptothiadiazoles, bisdithiocarbamates, dithiocarbamates, phosphorodithioates. No indication is given on a specific combination of the molybdenum complex with one or more of the mentioned organic sulfur compounds, nor on the amount of Mo contained in the lubricant compositions. The examples indicate an amount of complex comprised between 0.5 and 1.5% by weight in the lubricant, which corresponds to an Mo content comprised between 5 and 1,800 ppm in the lubricant. A too strong or too low Mo content is unsuitable for formulating a lubricant for a gear box. Indeed, problems of flaking or blocking of the synchronizers may result from this. The same applies for the selection and dosage of the sulfur and/or phosphor-sulfur additives.

Application WO 2005035700 discloses lubricant compositions comprising an organic molybdenum compound selected from molybdenum dithiophosphates or dithiocarbamates and an anti-wear compound which may be a dimercaptothiadiazole. This application does not disclose the combination of a specific molybdenum content with the use of a thiazole as an anti-wear and extreme pressure agent. The use of molybdenum in the form of dithiophosphates or dithiocarbamates is moreover capable of generating further problems of wear and/or blocking of the synchronizers, and possibly flaking. However, the compositions of the prior art based on molybdenum, sulfur and/or phosphorus relate to the field of anti-oxidants and anti-wear agents, mainly for formulating oils for internal combustion engines.

In particular, these compositions of the prior art do not have a specific dosage of element Mo, and a sufficient presence of sulfur and phosphorus allowing them to have both properties for protection against flaking, the wear of the synchronizers and avoiding blockings of the synchronizers in a satisfactory way. These compositions are therefore not adapted to the lubrication of gear boxes of automobile vehicles, in particular manual gear boxes. Among the known oils for manual gear boxes, borate oils have an excellent compromise between the different properties listed above. These oils may be formulated without any sulfur, phosphorus or phosphor-sulfur compounds, and up to now no technology based on sulfur, phosphorus or phosphor-sulfur additives gave the possibility of attaining the performance level obtained with borates as regards protection against flaking and wear of the synchronizers.

In spite of their excellent extreme pressure performances and of their many advantages, the use of borates is however not desirable since there is a risk of contamination of the lubricant by water. Indeed, inorganic borates being partly soluble in water, the amount of water present in the molecule may increase which has the effect of changing the structure of the borate. In the presence of a significant amount of water in the medium, the structure of the borate being thereby modified, they may crystallize and form crystals as knives with sizes greater than 100 nm. In this case, the borates may block the synchronization systems in the gear boxes.

The use of borate oils therefore requires a particular design of the manual gear boxes with a waterproof system, which has complexity and a cost which should desirably be avoided. Therefore there exists a need for oils for gear boxes of automobile vehicles, in particular manual gear boxes, giving both protection against the flaking phenomenon on the gear teeth, allowing limitation of the wear of the synchronizers and avoiding their blocking, allowing easy change of the gears, and insensitive to water (they may not contain borates or else a reduced level of borates).

The object of the present invention is lubricant compositions, comprising a molybdenum complex of the ester-amide type, combined with a sulfur-containing extreme pressure additive and a phosphorus-containing or phosphor-sulfur extreme pressure additive and to their use for lubricating gear boxes, in particular for automobile vehicles. A particularly relevant use relates to manual gear boxes of automobile vehicles.

SUMMARY

The object of the present invention is lubricant compositions comprising:

-   (a) an organic molybdenum compound, -   (b) one or more anti-wear and extreme pressure additives selected     from thia(di)azoles, -   (c) one or more phosphorus-containing and/or phosphor-sulfur     anti-wear and extreme pressure additives selected from phosphites,     phosphates, phosphonates, thiophosphates or thiophosphites.

The lubricant composition has a molybdenum mass content comprised between 90 and 350 ppm. Preferentially, the lubricant compositions according to the invention have a molybdenum mass content comprised between 100 and 200 ppm, preferentially between 140 and 180 ppm. Preferentially, the lubricant compositions according to the invention have a phosphorus mass content comprised between 500 and 700 ppm, still more preferentially between 520 and 650 ppm.

According to an embodiment, the lubricant compositions according to the invention comprise at least one thiophosphate, preferentially at least one dithiophosphate, preferentially at least one amine dithiophosphate, as a compound (c). According to a preferred embodiment, the lubricant compositions according to the invention comprise at least one thiadiazole, preferentially at least one dimercaptothiadiazole as a compound (b). The lubricant compositions according to the invention may comprise between 0.35% and 1% by mass of thiazole, preferentially between 0.35 and 1% by mass of dimercaptothiadiazole.

According to a preferred embodiment, the lubricant compositions according to the invention comprise as a compound (a), at least one organic complex of molybdenum, obtained by reaction:

-   -   (i) of a fat of the mono-, di-, or tri-glyceride or fatty acid         type,     -   (ii) of an amine source of formula (I)

-   -   wherein X1 and X2 are either O or else N, and n and m=1 when X1         or X2 is O, and n and m=2 when X1 or X2 is N,     -   (iii) a molybdenum source selected from molybdenum trioxide or         molybdates, preferentially ammonium molybdate, in a sufficient         amount in order to provide 0.1 to 20.0% of molybdenum based on         the weight of the complex.

Preferentially, the compound (ii) is diethanolamine or 2-(2-aminoethyl)aminoethanol. Preferentially, the fat (i) is a mono-, di- or tri-glyceride of fatty acids including from 4 to 28 carbon atoms, preferentially from 8 to 18 carbon atoms, or a fatty acid including from 4 to 28 carbon atoms, preferentially from 8 to 18 carbon atoms.

According to a preferred embodiment, the molybdenum complex (a) consists of at least one of the following compounds, either alone or as a mixture:

wherein X1 and X2 are either O or else N, and

n=1 when X1 is O and m=1 when X2 is O,

n=2 when X1 is N and m=2 when X2 is N,

wherein R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms, preferentially between 7 and 17 carbon atoms.

According to a more preferred embodiment, the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

wherein R1 is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms, preferentially between 7 and 27 carbon atoms.

According to another preferred embodiment, the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

wherein R1 is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms, preferentially between 7 and 27 carbon atoms.

The present invention also relates to the use of the composition described above for lubricating gear boxes, in particular of automobile vehicles. According to a preferred embodiment, the present invention relates to the use of the composition described above for lubricating manual gear boxes, in particular manual gear boxes for automobile vehicles.

DETAILED DESCRIPTION

Organic Molybdenum Compound: The lubricant compositions according to the invention may comprise any organic molybdenum compound soluble in oil, notably and not in a limiting way, molybdenum dithiophosphates and dithiocarbamates and various organic complexes of molybdenum such as molybdenum carboxylates, esters, amides, which may be obtained by reaction of molybdenum oxide or of ammonium molybdates with fats, glycerides or fatty acids, or with fatty acid derivatives (esters, amines, amides . . . ). Preferentially, the lubricant compositions according to the invention comprise complexes of molybdenum free of sulfur and of phosphorus, with ligands of the amide type, mainly prepared by reaction of a molybdenum source, which may for example be molybdenum trioxide, an amine and fatty acid derivative for example comprising from 4 to 28 carbon atoms, preferentially from 8 to 18 carbon atoms, such as for example fatty acids contained in vegetable or animal oils. The synthesis of such compounds is for example described in patents U.S. Pat. No. 4,889,647, EP0546357, U.S. Pat. No. 5,412,130, EP1770153.

These organic complexes of molybdenum may be obtained by reaction:

-   -   (i) of a fat of the mono-, di- or tri-glyceride or fatty acid         type,     -   (ii) of an amine source of formula (I):

-   -   wherein X1 and X2 are either O or else N and n and m=1 when X1         or X2 is O, and n and m=2 when X1 or X2 is N,     -   (iii) and of a molybdenum source selected from molybdenum         trioxide or molybdates, preferentially ammonium molybdate in a         sufficient amount in order to provide 0.1 to 20.0% of molybdenum         based on the weight of the complex. They generally comprise         between 7 and 8.5% by weight of molybdenum based on the weight         of the complex.

In particular, according to an embodiment, the organic molybdenum compound of the compositions according to the invention consists of at least one of the following compounds, alone or as a mixture:

wherein X1 and X2 are either O or else N, and

n=1 when X1 is O and m=1 when X2 is O,

n=2 when X1 is N and m=2 when X2 is N,

wherein R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms, preferentially between 7 and 17 carbon atoms.

According to an embodiment, the molybdenum complexes of the compositions according to the invention are prepared by reaction:

-   -   (i) of a fatty acid of the mono-, di- or tri-glyceride or fatty         acid type,     -   (ii) of diethanolamine or 2-(2-aminoethyl)aminoethanol,     -   (iii) and a molybdenum source selected from molybdenum trioxide         or molybdates, preferentially ammonium molybdate, in a         sufficient amount in order to provide 0.1 to 20.0% of molybdenum         based on the weight of the complex.

In particular, according to an embodiment, the organic molybdenum compound of the compositions according to the invention consists of at least one of the following compounds (IV) or (V) alone or as a mixture.

wherein R1 is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms, preferentially between 7 and 27 carbon atoms.

The content of organic molybdenum compound in the compositions according to the invention is adjusted so that the molybdenum mass content of said compositions is comprised between 90 and 350 ppm, preferentially between 100 and 200 ppm, even more preferentially between 140 and 180 ppm. A too low molybdenum content generates problems of synchronizer blocking and potential wear of the cone-ring assembly of the synchronizer. A too strong molybdenum content on the other hand has an unfavorable effect on flaking.

Thia(di)azoles: Thia(di)azoles are compounds which contain both a sulfur and a nitrogen atom in a ring of five atoms. Benzothiazoles are a particular type of thia(di)azoles. This term of thia(di)azole includes, in addition to the cyclic compounds containing a sulfur atom and a nitrogen atom per ring of 5 atoms, also thiadiazoles which contain sulfur and two nitrogen atoms in such a ring. These compounds may be non-substituted or substituted with hydrocarbon compounds which increase their solubility in oil.

According to an embodiment, the thia(di)azoles of the lubricant compositions according to the invention are non-substituted benzothiazoles, thiazoles, thiadiazoles. According to a preferred embodiment the thia(di)azoles of the compositions according to the invention are dimercaptothiadiazoles, for example 2,5-dimercapto-1,3,4-thiadiazole, 3,5-dimercapto-1,2,4-thiadiazole, 3,4-dimercapto-1,2,4-thiadiazole, 4,5-dimercapto-1,2,3-thiadiazole, 3-methylmercapto-, 5-mercapto-1,2,4-thiadiazole. All these compounds may be used alone or as a mixture. Typically, thia(di)azoles represent between 0.35 and 1% by mass of the compositions according to the invention. Preferentially, the compositions according to the invention contain between 0.35 and 1%, preferentially between 0.34 and 0.45% by mass of dimercaptothiadiazoles.

Phosphorus-Containing or Phosphor-Sulfur Compounds: Phosphorus-containing compounds of the lubricant compositions according to the present invention are anti-wear and extreme pressure additives such as phosphates, phosphites, or phosphonates. These terms both designate phosphoric, phosphorous, phosphonic acids, their mono-, di- and tri-esters, for example alkyl phosphates, alkyl phosphonates, alkyl phosphonates, and their salts, for example amine salts. The phosphor-sulfur anti-wear and extreme pressure additives used in the present invention are (mono- or di-)thiophosphates and thiophosphites, these terms including thiophosphoric and thiophosphorous acids, the esters of these acids, their salts, dithiophosphites and dithiophosphates.

According to a preferred embodiment, the phosphor-sulfur anti-wear and extreme pressure additives of the compositions according to the invention are thiophosphates, corresponding to the formula (VI)

wherein X3 and X4 are independently of each other S or O, one of them at least being S, R3 and R4 are either hydrogen or alkyl groups having between 1 and 22 carbon atoms, M is a metal of the IIA, III, VA, VIA, IB, VIB, VIII Groups of the Periodic Table, n being the valence of said metal, or else M is an ammonium formed from a primary, secondary or tertiary amine of formula (R5)(R6)(R7)N, wherein R5, R6, R7 are either hydrogen or an alkyl group including from 1 to 18 carbon atoms and then n=1.

More preferred compounds are the dithiophosphates (X3 and X4 are sulfur), preferentially of zinc or of an amine. Amine dithiophosphates are more preferred compounds. As examples of phosphor-sulfur anti-wear and extreme pressure additives, mention may be made of monobutylthiophosphate, monooctylthiophosphate, monolaurylthiophosphate, dibutylthiophosphate, dilaurylthiophosphate, tributylthiophosphate, trioctylthiophosphate, triphenylthiophosphate, trilaurylthiophosphate, monobutylthiophosphite, monooctylthiophosphite, monolaurylthiophosphite, dibutylthiophosphite, dilaurylthiophosphite, tributylthiophosphite, trioctylthiophosphite, triphenylthiophosphite, trilaurylthiophosphite and salts thereof. Examples of esters of thiophosphoric acid and of thiophosphorous acid are those obtained by reaction with a nitrogen-containing compound such as ammonia or an amine, or zinc oxide or zinc chloride.

Preferentially, the amount of these additives is adjusted so that the phosphorus mass content of the oils according to the invention is comprised between 500 and 700 ppm, preferentially between 520 and 650 ppm. A too low content of the anti-wear and extreme pressure element (sulfur and phosphorus) will generate flaking problems. Moreover, a too strong content of anti-wear and extreme pressure elements, (as well as of a friction modifier, including an organic molybdenum compound), will have an unfavorable effect on changing gears: the cone-ring friction coefficient will be too low, which prevents synchronization of the gears and therefore changing of the gears.

Moreover, it is desirable for environmental reasons to limit the sulfur and phosphorus content in the lubricant compositions to what is required. This, in combination with the molybdenum content of the lubricants according to the invention gives the possibility of obtaining both better anti-flaking, synchro-anti-wear properties and of avoiding synchronizer blockings. The most efficient compromise between these 3 properties therefore depends on a specific dosage of the friction modifier, anti-wear and extreme pressure compounds and therefore of the Mo, S and P elements from these compounds.

Bases: The compositions according to the invention may contain any type of animal or plant, synthetic or natural mineral lubricant base, adapted to their use. The base oil(s) used in the compositions according to the present invention may be oils of mineral or synthetic origin of the groups I to V according to the classes defined in the API classification (or their equivalents according to the ATIEL classification), as summarized below, alone or as a mixture.

Saturated product Sulfur Viscosity content content index Group I Mineral oils  <90%  >0.03% 80 ≦ VI < 120 Group II Hydrocracked ≧90% ≦0.03% 80 ≦ VI < 120 oils Group III ≧90% ≦0.03% ≧120 Hydrocracked or hydro- isomerized oils Group IV PAO Polyalphaolefins Group V Esters and other bases not included in the bases of Groups I to IV

The mineral base oils according to the invention include all types of bases obtained by atmospheric and vacuum distillation of crude oil, followed by refining operations such as extraction with a solvent, deasphalting, deparaffining with a solvent, hydrotreatment, hydrocracking and hydroisomerization, hydrofinishing. The base oils of the compositions according to the present invention may also be synthetic oils, such as certain esters of carboxylic acids and alcohols, or polyalphaolefins, the polyalphaolefins used as base oils, are for example obtained from monomers having from 4 to 32 carbon atoms (for example octane, decene), and a viscosity of 100° C. comprised between 1.5 and 15 cSt. Their average weight molecular mass is typically comprised between 250 and 3,000. Mixtures of synthetic and mineral oils may also be used. There is no limitation as to the use of such and such lubricant base for producing the compositions according to the invention, if not that they should have properties, notably of viscosity, viscosity index, sulfur content, resistance to oxidation . . . adapted to a use in a gear box, in particular for automobile vehicles, in particular a manual gear box.

Preferentially, the lubricant bases represent at least 50%, preferentially at least 60%, or further at least 70% by mass of the lubricant compositions according to the invention. Typically, they represent between 75 and 90% by mass of the compositions according to the invention. Preferentially, the lubricant compositions according to the invention comprise mineral bases of Group I and/or III, or synthetic bases of Group IV according to the API classification.

Other Additives: The lubricant compositions according to the invention may also contain any type of additive adapted to their use, for example amine or phenol antioxidants such as diphenylamines, or phenols substituted on at least one of their ortho positions with alkyl groups, detergents, for example sulfonates. Agents for improving the viscosity index (VI enhancing agents) are preferentially present at contents comprised between 5 and 25% by mass, so as to impart viscosimetric properties adapted to the use in a gear box, in particular an automobile gear box, preferentially a manual gear box, such as for example polymethacrylates (PMA), polyisobutenes (PIB), or fatty acid esters . . . .

EXAMPLES

The mass compositions and performances as regards synchro wear, synchro blocking, flaking of the prepared lubricant compositions are shown in Table 1 hereafter.

The flaking tests were carried out under the following conditions:

-   BCFP Sermes Bench -   Renault JR5-125 gear box, 1 pair of differentials 14×63, secondary     shaft 8200280045 and ring 8200280134, 3 pairs 28×37 of primary     shafts 8200107846 and idler pinions 3° 7700114048 -   2.3 liters of oil, oil temperature 110° C. -   Input torque: 148 mN -   Primary speed 3,000 rpm -   Duration: 3 phases of 142 hours -   Every 142 hours, changing of the primary shaft, of the idler pinion     3° and the roller bearings.

Evaluation of the flaked surface:

-   Final score after 426 hours of the pinion/differential ring pair, -   Score after 142 hours of 3 pairs 28×37 primary shafts/idler pinion     3° -   Depending on the result of the score of these parts, it is said to     pass (satisfactory scores) or to fail (too large flaked surface).

The tests for blocking the synchronizers were carried out on a cone-ring pair under the following conditions (SYNC-40 procedure):

-   Threaded brass ring of 54 mm, e.g. ref 7700 708 152 or 7700 869 430 -   Cone of idler pinion gear box JXX, stoned rectified carbonitride     steel, -   e.g. ref 7700 867 612 or 7700 740 880 -   Oil: 250 ml of oil, oil level at the middle of the pinion and of the     ring -   SAE2/A Machine SAE/2 synchro adapter -   I=0.155 m²/kg -   N=300 rpm -   F=60 daN -   T=6s (consecutive period between two consecutive braking operations) -   n=10,125 gear changing cycles (21 hours)

The synchro blocking test is passed, if, during 10125 gear-changing cycles, the number of cycles wherein disengagement between the cone and the ring requires the application of a counter-torque of more than 2 mN is at most 100 cycles.

The synchronizer wear tests were carried out on a cone-ring pair under the following conditions (procedure SYNC-13, SAE 2-A)):

-   Threaded brass ring of 54 mm, e.g. ref 7700 708 152 or 7700 869 430 -   Cone of idler pinion gear box JXX, stoned rectified carbonitride     steel, -   e.g. ref 7700 867 612 or 7700 740 880 -   Huile: 125 ml of oil, oil level of the lower portion of the ring -   SAE2/A Machine SAE/2 synchro adapter -   I=0.155 m²/kg -   N=600 rpm -   F=60 daN -   T=3.5s (consecutive period between two consecutive braking     operations) -   n=20,000 gear changing cycles (20 hours)

At the end of these 20,000 cycles: the axial wear of the synchronizer ring/gear cone pair is measured in mm. It should be at most of the order of 0.30 mm in order to be acceptable (pass). A wear of less than 0.15 mm is an excellent performance. A wear of more than 1 mm is disqualifying (guard compensation).

Discussion: The oils A and B are oils according to the invention: the oils C and D are borate oils, sensitive to water. The oils A and B have a performance level as regards wear of synchronizers, equivalent to that of borate oils, and pass the tests of blocking and of flaking in the same way. The oil E contains the same anti-wear and extreme pressure additives as oil A, also with phosphorus-containing compounds of the phosphite/phosphate type; this oil E does not contain any friction modifier with molybdenum. The wear of the synchronizers is at an unacceptable level (0.84 mm).

The oils F, G, H have the same additivation in sulfur-containing and phosphor-sulfur anti-wear and extreme pressure agents as the oils according to the invention, but contain various friction modifiers without molybdenum. The wear of the synchronizers is very significant with these oils. The oils I and L have the same additivation as regards sulfur-containing and sulfur-phosphor anti-wear and extreme pressure agents as the oils according to the invention, and contain a friction modifier with molybdenum of the ester amide type.

The ester Mo content of the oil I is 400 ppm, and this oil fails as regards flaking. The mass Mo content of the oil L is 80 ppm, and this oil fails as regards synchroblocking.

Oil J has the same additivation of sulfur-containing and phosphor-sulfur anti-wear and extreme pressure agents as the oils according to the invention, but do not contain any molybdenum. A fatty acid mono-ester is present as a friction modifier. This oil fails as regards synchronizer blocking.

The oil K has the same additivation of sulfur-containing and phosphor-sulfur anti-wear and extreme pressure agents as the oils according to the invention, and does not contain any molybdenum. It does not contain any friction modifier. This oil fails as regards synchroblocking.

The oils M and N do not contain any thiazole as a sulfur-containing compound. The oil M is also free of molybdenum. These oils have obtained a particularly catastrophic result as regards flaking. It should be noted that these oils do not contain any dimercaptothiadiazole.

TABLE 1 Mass Composition and Properties A B C D E F G Friction Mo complex 0.20 0.20 Modifiers Borate additive 8.70 8.70 Polysulfide ester 1.00 Fatty acid ester 1.00 Fatty acid monoester Anti-wear and phosphates/phosphites 0.20 extreme dimercaptothadiazole 0.40 0.35 0.40 0.40 0.40 pressure dithiophosphates 0.90 0.85 0.90 0.90 0.90 additives Other antioxidant 0.90 0.80 0.90 0.90 0.90 VI enhancer 21.00 9.00 11.00 19.50 21.00 21.00 21.00 detergent Bases Mineral Group I 4.80 61.50 31.00 5.30 4.80 4.80 Mineral Group III 71.80 20.00 35.00 71.80 71.30 71.00 71.00 Synthetic Group IV 7.30 14.30 ppm of Mo 160 160 0 0 0 0 ppm of P 610 535 625 610 610 Flaking pass pass pass pass Wear/ pass/ pass pass/ pass/ fail/ fail/ fail/ value in mm 0.12 0.08 0.14 0.84 1.03 0.49 Synchro blocking pass pass pass pass pass pass pass Total 100.00 100.00 100.00 100 100.00 100.00 100.00 H I J K L M N Friction Mo complex 0.50 0.10 0.20 Modifiers Borate additive Polysulfide ester Fatty acid ester Fatty acid monoester 1.00 Anti-wear and phosphates/phosphites 1.00 1.90 1.90 extreme dimercaptothadiazole 0.40 0.40 0.40 0.40 0.40 pressure dithiophosphates 0.90 0.90 0.90 0.90 0.90 1.20 1.20 additives Other antioxidant 0.90 0.90 0.90 0.90 0.90 VI enhancer 21.00 21.00 21.00 21.00 21.00 11.00 11.00 detergent 1.20 1.20 Bases Mineral Group I 4.80 4.80 4.80 4.80 4.80 76.70 76.50 Mineral Group III 71.00 72.00 71.00 72.00 72.00 Synthetic Group IV 8.00 8.00 ppm of Mo 0 400 0 0 80 160 ppm of P 610 610.4 610 610 Flaking fail fail fail Wear/ fail/ pass/ pass/ pass/ pass/ pass pass value in mm 0.75 0.13 0.20 0.12 0.22 Synchro blocking Pass pass fail fail fail pass pass Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Mo Complex: an organic molybdenum complex with amide ligands. 

1. A lubricant composition comprising: (a) an organic molybdenum compound, (b) one or more anti-wear and extreme pressure additives selected from thia(di)azoles, (c) one or more phosphorus-containing and/or phosphor-sulfur anti-wear and extreme pressure additives selected from phosphites, phosphates, phosphonates, thiophosphates or thiophosphites; the lubricant composition having a molybdenum mass content comprised between 90 and 180 ppm.
 2. The lubricant composition according to claim 1 having a molybdenum mass content comprised between 140 and 180 ppm.
 3. The lubricant composition according to claim 1, having a phosphorus mass content comprised between 500 and 700 ppm.
 4. The lubricant composition according to claim 1, comprising at least one dithiophosphate as compound (c).
 5. The lubricant composition according to claim 1, comprising at least one dimercaptothiadiazole as compound (b).
 6. The lubricant composition according to claim 5, comprising between 0.35 and 1% by mass of dimercaptothiadiazole.
 7. The lubricant composition according to claim 1, comprising, as a compound (a), at least one organic complex of molybdenum, obtained by reaction: (i) of a fat of the mono-, di- or tri-glyceride or fatty acid type, (ii) of an amine source of formula (I):

wherein X1 and X2 are either O or else N, and n and m=1 when X1 or X2 is O and n and m=2 when X1 or X2 is N, (iii) and of a source of molybdenum selected from molybdenum trioxide or molybdates in a sufficient amount in order to provide 0.1 to 20.0% of molybdenum based on the weight of the complex.
 8. The lubricant composition according to claim 7, wherein the compound (ii) is diethanolamine or 2-(2-aminoethyl)aminoethanol.
 9. The lubricant composition according to claim 7, wherein the fat (i) is a mono-, di- or tri-glyceride of fatty acids including from 4 to 28 carbon atoms, or a fatty acid including from 4 to 28 carbon atoms.
 10. The lubricant composition according to claim 7, wherein the molybdenum complex (a) comprises at least one of the following compounds, either alone or as a mixture:

wherein X1 and X2 are either O or else N, and n=1 when X1 is O and m=1 when X2 is O, n=2 when X1 is N and m=2 when X2 is N, wherein R1 and R2 are fatty hydrocarbon chains comprising between 3 and 27 carbon atoms.
 11. The lubricant composition according to claim 7, wherein the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

wherein R1 is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms.
 12. The lubricant composition according to claim 7, wherein the molybdenum complex (a) consists of at least one of the compounds corresponding to the following formula:

wherein R1 is a fatty hydrocarbon chain comprising between 3 and 27 carbon atoms.
 13. A method for lubricating gear boxes comprising bringing into contact a composition according to claim 1 with a gear box.
 14. The method according to claim 13, wherein the gear box is a manual gear box.
 15. The lubricant composition according to claim 1, wherein the organic molybdenum compound is selected from the group consisting of molybdenum dithiophosphates, molybdenum dithiocarbamante and organic complexes of molybdenum.
 16. The lubricant according to claim 15, wherein the organic complex of molybdenum is selected from the group consisting of molybdenum carboxylates, molybdeum esters, molybdenum amides. 